Method and apparatus for the operation of an automatically controlled synchronous machine

ABSTRACT

The operation of an automatically controlled synchronous machine is controlled by controlling the vector of the stator current circulation by means of two components which can be varied independently of each other. One of these components, namely, the torque-generating component, is always perpendicular to the axis of the rotating field, and the other, the field-generating component, always parallel to the axis of the rotating field. In a drive of this type, which is particularly well suited for a transmissionless cement mill, full torque at stand-still, starting without chatter and full utilization at rated operation are obtained.

United States Patent [191 Bayer et a1.

" m] f 3,775,649 Nov. 27, 1973 v 221 Filed:

[ METHOD AND APPARATUS FOR THE OPERATION OF AN AUTOMATICALLY CONTROLLEDSYNCHRONOUS MACHINE v [75] Inventors: Karl-Heinz Bayer, Erlangen;

Hermann Waldmann, Weiher;

Manfred Weibelzahl, Erlangen, all of Germany I ['73] Assignee: SiemensAktiengesellschaft,

Munich, Germany June 27, 1972 21 App1.No.:266,t3 13 [30] ForeignApplication Priority Data June 29, 1971 Germany P 21 32 178.8

[52] US. Cl. 318/188, 318/227 [51] Int. Cl. H02p 7/36 [58] Field ofSearch 318/227, 171, 1-75, 318/188 [56] References Cited UNITED STATESPATENTS 3/1968 Boudigues 318/175 X 3,694,716 9/1972 Eland ..318/175Primary Examiner-B. Dobeck Attorney-Hugh A. Chapin [5 7 ABSTRACT Theoperation of an automatically controlled synchronous machine iscontrolled bycontrolling the vector of the stator current circulation'by means of two components which can be varied independently of eachother. One of these components, namely, the torquegenerating component,is always perpendicular to the axis of the rotating field, and theother, the fieldgenerating component, always parallel to the axis of therotating field. in a drive of this type, which is particularly wellsuited for a transmissionless cement mill, full torque at stand-still,starting without chatter and full utilization at rated operation areobtained.

17 Claims, 9 Drawing Figures Sofan 318/175 PATENmrmvzv m5 SHEET 1 [IF 4T. C. TRANSFORMATION CIRCUlT Fig.2

PATENI nnuvm 197s SHEET 2 [1F 4' PATENTED HUVZ 7 I375 SHEET 3 UF 4 Fig.7

PATENTED U 3,775,649

SHEET u [If 4 F.C. FLUX COMPUTER T. C. TRANSFORMATIONCIRCUIT sinoC sasus 1 METHOD ANDAPPARA TUS FOR THE OPERATION OF AN AUTOMATICALLYCONTROLLED SYNCHRONOUS MACHINE FIELD OF THE INVENTION BACKGROUND OF HE'IvENTIoN A converter-fed synchronous. motor for a transmission-less,cement mill drive has been known, for example, as. describedtin themagazineBrown-Boveri-Mitmatic control, is provided "in principle withthe same controlbehavior as a d-c commutator motor, without being.subject to thelimitations imposed by the use of a mechanical commutator.In this known drive, the amplitude of ,the stator current is used-astheprincipal controlled quantity and the angle between the vector of thestator current circulation and the rotor as well as the excitationcurrent are adjusted as a function of the preset stator amplitude bymeans of function generators in such a manner that the resulting linkingof the stator flux always remains at, its nominal value and the functiongenerators, and only in the stationary state of the machine'as a.coupling between the field and the stator current during transition fromone stationary condition to another leads to overvoltages orrotoroscillations. A further limitation of this known arran'gemerit residesinthe fact that it permits basically only operation with cos I 1 whereasit is frequently desirable to deviate from this condition in order tomake a maximum torque of the machine available or to preventovervoltages in the event of load shocks.

Accordingly, it is an object of the invention to provide an improvedtechniquefrom the dynamic pointof view for controlling orregulatinga'converter-fed, automatically controlled synchronous machine, in whichthe active as well as the reactive component of the stator current,i.e., its torque-generating and its fieldgenerating components, can bepreset directly and in dependently of each other.

SUMMARY OF THE INVENTION Briefly, the invention provides a methodandapparatus by which the two components which'determine the instantaneousposition of the rotating-field axis are ascertained directly, orby meansof a field simulation, and the vector of the stator current circulationis preset current components from two orthogonal components determiningthe instantaneous position of the rotor axis and two stator-referencedorthogonal stator current components. The tow rotor-referencedorthogonal components are then transferred by means of field simulation,.into two rotor-referenced orthogonal field components which arecombined with two rotor position components to form twostator-referenced orthogonal components which determine theinstantaneous position of the axisof the rotating field. Thus, a biaxialforward and back transformation of the input and output quantities ofthe field simulation take place.

According to a further embodiment of the invention,

V .a vector rotatorcanbe used in ,the above-mentioned teIlungen,-l9.70,p. 121 to- I29, which,,through auto- 15' component. transformations,which consists of two summing amplifiers and four multipliers,theoutputs of which are connected in pairs with the input of oneamplifier each.

In one embodiment, the field simulation can be made with a minimum ofamplifiersby use of two differential amplifiers with negative resistorfeedback, one of whichis driven by the stator current component lying inthe direction of the rotor axis and a signal quantity proportional tothe excitation current, and the other by the stator currentcomponentwhich is perpendicular to the rotor axis. For synchronousmachines equipped with damper windings, negative-feedback branches areprovided each of which connects the output of a differential amplifierwithits input andlconsists of a capaciorder to assure constant gain,i.e., for adaption purposes, the preset component which is perpendicularto by means of two reference components which canbe variedindependentlyof each other. These latter reference components are suchthatone is always perpenthe axis of the rotating field is the outputsignal of a quotient generator whose dividend input is connected withthespeed=control and'whose divisor input is driven by a quantity which isproportional to the absolute value'of the rotating-field vector.

According toafurther embodimentof the invention, in order'to keep theexcitation constant, regardless of the mechanical load ofthe synchronousmachine, a flux control is provided. This flux control is fed, as theactual value, a quantity proportionalto the absolute value of therotating-field vector. In order to' improve the dynamics of thefluxcontrol, it is advisable in thisconnection if an excitation currentregulator is subordinated to theflux control:

Accordingtoa further embodiment of the invention,

the input signal of the excitation current regulator determines thepreset component that is parallel to the axis of the fieldiin ordertoassist theexcitationcurrent regulator in the event'of a rapid build-upor decay of the field.

' DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a vector diagram of thestator winding axes of a three-phase synchronous machine;

FIG. 2 illustrates a block diagram of a field-oriented control systemaccording to the invention;

FIG. 3 illustrates a circuit diagramof a vector rotating according totheinvention;

FIG. 4 illustrates a circuit diagram of a transformation circuitaccording to the invention for transforming the component voltages of athree-phase system into corresponding component voltages of a two-phaseorthogonal system;

FIG. 5 illustratesa circuit fora transformation circuit to transformabiaxial Orthogonal component system into a correspondingtriaxialcomponent system; FIG. 6 illustrates'a circuit diagram of a fluxconputer according to' the invention;

FIG. 7 illu's'trat es a circuit diagram of a vector analy 'zer usedinthe flux computer of FIG. 6;

FIG. 8 illustrates a block diagram of a field-oriented control systemaccording to the invention for a transmissionlesstubular milldrive; and

FIG. 9 illustrates a circuit for a current regulator according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the statorwinding axes of a three-phase synchronous machine are designated R, Sand T. At a particular instant of time, the axis P of a rotor rotatingin the direction indicated by the arrow forms an angle d with the axisof the stator winding R within a" stationary orthogonal coordinatesystem having axes b and a,}wherein the axis a coincides with the statorwinding axis R. At the same instant, the instantaenced coordinate systema, b, thestator current circulation is defined by the components i andi,,. The component I represents the torque-generating component and Ithe field-generating component of the stator current. For an operationalstate in which cos P 1, I would have the value 0, and the stator currentwould accordingly be a purely active current.

Referring to FIG. 2, a three-phase system N feeds, via controlledconverters 1, 2, the rotor and the stator windings of a synchronousmachine 3. The control line of the converter 1 feeding the rotor areacted upon by a fiux control 4 into which a constant quantity 45* is setas a reference value. A flux computer 5,-described below, supplies, viaa terminal 6, a quantity which is proportional to the absolute value I(b of the rotating-field vector as the actual value for the flux control4'while also supplying, via terminals 7, 8,two component voltages,designated sinB and cosB, which define the instantaneous position of therotating-field axis (F) in the stator reference coordinate system a, b.In order to ef-' to the excitaat terminals 10 and l 1 twostator-referenced orthogonal stator current components i,, and i,, whichare obtained from the three stator phase currents by means of atransformation circuit 12; and

at terminals 13 and 14, two components sin a and cos a which define therespective rotor position p in the stator-referenced coordinate systema, b and which are supplied by a digitally operating threephasegenerator 15 via a further transformation circuit l6. The digitalthree-phase generator 15 is known per se and is'des c ribed, forinstance.in the German published Patent application 1,563,741. Thisgenerator 15 consists essentially of a counter,

' a stepping switch, a distribution gate and a digitalto-analogconvertersystern'and delivers three sinusoidal output voltageswhich areshifted I20 electrical degrees with respect to each other and whoseperiod is inversely proportional to the frequency of an input pulsesequence fed thereto. The digital threephase generator 15 is fed on theinput side from a galvano-magnetic (magneto-resistive) pulse generator16', for instance, in the form of a field plate" or a Hall effectgeneratonwhich is actuated in turn by a pulse dise17 coupled with therotor of the synchronous machine 3 and in whose periphery smallpermanent magnets are embedded at regular intervals, the number of whichis an integral multiple of the number of poles of the synchronousmachine 3.

The system N also includes a vector rotatorVDl having terminals D1 andD2 to which are delivered two reference signals I and I which can bepreset at will for the field-oriented stator current components I andI,, (see FIG. 1). Two other input terminals D3 and D4 of the vectorrotator VDl are connected with the output terminals 7 and 8 of the fluxcomputer 5 to receive I the components sin B and cos B which determinethe position of the axis (F) of the rotating field. As indicated inblock symbol, the vector rotator VDl ad vances the input vectordescribed by the quantities I and I by the angle B, i.e., the vectorrotator VDl represents the following relation between field-referencedand stator-referenced preset values, which can be derived from FIG. 1:

The stator-referenced preset values i.,* and i,,* which appear at thetwo output terminals D5 and D6 of the vector rotator VDl, aretransformed via a transformation circuit 18 into three phase-currentreference values and are compared in the mixing stages 19 with the threecorresponding actual values of the stator current. Three correspondinglyassociated phase current regulators 20, of which only one is shown forthe sake of simplicity, then bring about agreement between the actualvalues and the reference values. I

Referring to FIG. 3, the vector rotator VDl consists of two summingamplifiers 21 and 22, which are fed the output voltages from fourmultipliers 23 to 26. All resistors connected to theinputs,.respectively marked with and of the amplifiers 21 and 22 are ofthe same size. The multipliers 23m 26 are connected in pairs with theinput terminals D1 to D4. If the input terminal D1 is connectedaccording to the arrangement of FIG. 2 with the torque-generating presetreference component I of the stator current, i.e. the one per- D6, whichare sum angle.-

pendicular tothe axis of the rotating field and the input terminal D2 isconnected with the field-generating reference component 1 i.e., theonepreset parallelto the axis of therotating field and if the fieldcomponents sin Band cost? are fed to the input terminals D3 and D4,voltages will appear at the output terminals D5 and proportional to thecosine and sine of the (B an" [mi/m1) where the sum of the squares oftheir magnitude corresponds to the sum ofithe squares of the magnitudeof the input quantities 1 and I,,*@ With this circuit-con- :n e'ction ofthe vector rotator VD1, the interrelation fgivenabove is'thereforerealized.

' Referring to FIG. 4, the internal circuit design of .the

transformation circuits, designated12 and 16 infElG.

2', for transforming the component voltages. of athreephase system intocorresponding component voltages of a two-phase orthogonalsystem,describe the same vector; The transformation circuit consists of twoamplifiers 27,28 to which the component voltages designated imi and'iare fed The transformation is carried out by-means of transformationrules knownper se, for which purposes the load resistors of theamplifiers 27 and 28 have the resistance ratios indicated in FIG. 4.

' ture circulation into two components wich are assumed to rotate withthe rotor. In the following, the subscript d is alwaysused withreferenceto a component in the direction of the rotor axis P (seeFIG. 1) and the subscript q with reference to a component transverse tocurrent. This current i 'is fed to the flux computer 5 at the inputterminal 9. v

The type of field simulation shown in FIG. 6 in the d, q coordinatesystem is known through German published Patent Application 1,917,567and will therefore be repeated here only with regard to its essentialfeatures. The differential amplifier 32 has three feedback paths: Y

one via the resistor R1 whose size corresponds to the value of the maininductance lh of the field winding; another via the series circuit ofthe resistor R2 and the capacitor C which serves to simulate the dampingcircuit associatedwith the longitudinal axis;and a v i anotherviaia'multipler 34 which canbe provided to take into accounttheinfluence of saturation: lf'one =de notes withr theohmic resistance ofthe damp- '..ing circuit and with 1,, its strayinductance, with tance ofthe series circuitwhich provides negative feedbackfor thedifferentialamplifier 32,it can be shown by setting the coefficient rHQ, and i V R2 that the differential amplifier 32 with its feedbackcircuit elements R1,,,R2 andfC simulates the differential equation forthe fieldv component (15,,

. extending in the longitudinal direction of the rotor 1 axis, which inoperator notation (p d/a't) reads:

For the differential amplifier 33, or the field component extendingtransverselyto the longitudinal axis of the rotor the same analogousrelation applies. It is essential that in this kind of field simulation,only a single respective amplifier is required to simulate the fluxcomponents (h and (I), and that all parameters of the exciterand thedamping windings can be adjusted indethe rotor'axis, i.e. ,'in thedirection ofthe pole gap axis. 1

First, the two stator-referenced orthogonal stator current components iandi arriving at terminals 10,

11 are delivered 'to terminals D1, D2 of a second vector rotator VD2which is also fed. two components sina, cosa determiningtheinstantaneous rotor position via the terminals 13, 14 and inputterminals D3, D4. These components i, and i,, are then transformed bythe vector rotator VD2 into two corresponding, but rotor referencedcurrent components i and 11,, which appear at the output terminals D5and D6. The circuit-wise internal design of the vector rotator VD2corresponds to the and 33 which are used. to simulate the field. Thedifferential amplifier 32, which is provided for the simulation of theflux in the longitudinal direction of the rotor axis, is also fed acurrent i proportional to the excitation pendently of one another eachbya separate component.

In order to simulate the,in fluence of saturation, the output voltagesand d2,, corresponding to the fluxes of' the longitudinalandtransver'salaxegof the two differential amplifiers 32 and 33 aresquared in a multiplier arrangement 36 and 37, respectively, and addedin a mixing stage 38, for instance in the form of a summing amplifier,so that the square of the absolute value of the field vector composed ofthe two field components and (15 is formed. The output of the mixingstage 38 acts via a threshold stage upon the inputs 39 and 40 of themultipliers 34 and 35 which are arranged in an additional feedbackcircuit of the amplifiers 32, and 33. The threshold stage consists of anamplifier 41 whose gain is adjustable through a variable input resistor42 and in whose input circuit a biased threshold amplifiers 32 and 33.Thus, the output voltages of these multipliers 34, 35 act in anegative-feedback sense on the two field simulation amplifiers 32 and33. I The saturation simulation described above functions as follows:

Up to a certain value of the resulting total flux, the responsethreshold of the diode 43 is not exceeded R2,, the ohmic resistance andwith C,, the capaciby the output voltage of the mixing stage 38. A zerovoltage then exists atthe inputs 39 and 40 of the multipliers 34 and 35and no negative feedback takes placedue to output signals of themultipliers 34 and 35. This corresponds to the unsaturated acondition'of the machine. If the response threshold of the diode 43 is'exceeded, a square-law change of the degree of negative feedback takesplace due to the multipliers 34 and 35 arranged in the negative feedbackpaths. The actual magnetization characteristics can thereby besimulated. Thus, by changing the variable part of the voltage divider, Jthe set-in point'of the satura'tio'n can be set largely at will and withsufficient fidelity, and by varying the input resistor 43, the curvatureof the magnetization curve in the saturated region can be similarly'set.It is essential that in taking saturation into ,consideration one alwaysstarts out from the'vectorialsum of the two field components (1).; and4),. The rotor referenced field component voltages (1),, and tb are nowfed to the input terminals 44 and 45 of a vector analyzer VA,which hasthe purpose of forming at its output terminal 46, a voltage proportionalto the absolute value of the field vector, and at its output terminals47 an d'48 a voltage proportional to the sine and cosine of the anglebetween the rotor axis P and the flux axis F (c.f. FIG. 1). The twocomponent'voltages at the outputs 47 and 48 would then define in the d,q

coordinate system, a unit vector-which always points in the directionofthe rotating field. By means of a further vector rotator VD3, which isloaded on the input side in the manner of the vector rotator VDl andtherefore causes an advance of the vector fed to its terminals D1 andD2, two voltages are finally obtained at its output terminals D and D6which are proportional to the cosine and sine of the angle B whichencloses the rotating field axis F and the coordinated axis a which isfixed with respect to the stator.

Referring to FIG. 7, the vector analyzer VA consists of two quotientgenerator 49 and 50, whose dividend inputs are connected with theterminals 44 and 45, to which voltages proportional to the respectiveorthogonal components 41,, and dz, of the rotating-field vector 41 areapplied. The outputs of the quotient generators 49 and 50 are squared bymeans of two multipliers 51 and 52, the outputs of which are added in amixing stage 53. The input of this mixing stage 53 is further fed,subtractively, with a constant voltage E. This volt- 7 age E is avoltage with the magnitude 1, Le, a so-called unit voltage. The outputof the mixing stage 53 drives an integrator in the form of a PI (Poportionalintegrator) control 54, whose output is connected with thedivisor inputs of the quotient generators 49 and 50. For reasons ofstability, the PI control 54 is provided with a limit device 55, forinstance, in the form of a limiting diode, which limits the outputvoltage of the integrator on one side to zero and thus allows onlypositive values of this output voltage.

If the output quantity of the Pl control 54 is designated with x, and ifone takes into consideration the known fact that the output quantityof aPI control stops changing only when the sum of its input quantitiesvanishes, the vector analyzer V A reaches its stationary, i.e., thebalanced state, when the following relation applies:

. (t n/ 0 (tin/J0 E The outputquantity of the proportional integrator 54then corresponds exactly to the absolute value I 4) l of therotating-field vector. In this automatically produced stationarycondition, voltage appear at the terminals 47 and 48, which areconnected with the outputs of the quotient generators 49 and 50,:ofthe'magnitude Voltages can therefore be taken off at the outputterminals 46 to 48, which are proportional to the'absolute value of therotating field vector, as well'as to the sine and cosine of itsangle winthe d, 4 coordinate system.

Referring to FIG. 8, wherein like reference characters'indicate likeparts as above,-an example of an embodiment of the invention isshowinwhich is specifically. designed for the speed control of atransmissionless tubularmill'drive. The synchronous machine 3, which isconstructed in the form of a ring motor and whose rotor is mounteddirectly on the grin g drum, is fed from the three-phase system N via adirect converter 2, which-consists of three piars of three-phase bridgecircuits which are connected in anti-parallel and contain thyristors, ofwhich each pair is assigned to one stator phas connection. Thethyristors are triggered by means of control units St, which areappropriately driven by the'phase current controls 20. The arrangementaccording to FIG. 8 is essentially thesame as that of FIG. '2, with theaddition that to the torque control shown in FIG. 2, a speed control 56is superimposed whose output signal determines the reference-valuecomponent I which is perpendicular to the rotatingfield axis F. Theactual value of the speed control 56 is obtained from afrequency-voltage converter 57 which is supplied on an input side with apulse sequence from the pulse generator 16'. The reference value of thespeed control 56 is tapped off at-a potentiometer 58 as 'a d-c voltagewhich can be preset at will. In order to keep the control loop gainconstant, regardless of possible fluctuations of the magnitude of therotating-field .excitation current regulator 60 is subordinated to theflux control 4 in such a manner that the output signal of the fluxcontrol 4 constitutes the reference value of the excitation currentregulator 60. The actual valueof the excitation current i, is suppliedby a d-c converter 66 arranged in the exciter circuit, which isconnected on the secondary side also to the input terminal 9 of the fluxcomputer 5.

The field-oriented pre-setting of the stator current components opens upthe possibility of assisting the excitation current control, whichnaturally has a large time constant, in the event of load jumps,i.e.,.when

going from one stationary state to another, and of achieving thereby amore rapid transition while avoiding, in particular, undesireableovervoltages. To this end, the control deviation, which properly shouldbe removed by the excitation current regulator 60, i.e., the differencebetween the excitation current reference value i,.* and'the actualexcitation current value 1'... is fed via a terminal 64 to the input D2of the vector rotator VDl, which determines the stator current referencecomponent that is parallel to the field. In the stationary 7 condition,the input quantity of the excitation current regulator 60. is zero, andtherefore also the fieldparallel component of the stator. current; thesynchronous machine being operated with cos P I. If however, forinstance, due to load jumps, a temporary decrease or increase of theflux of the machine occurs (which thefiux control attemptsto compensatebut cannot do so fast enough because of the relatively large inertia ofthe excitation current control circuit subordinated thereto), a controldeviation will temporarily appear at the input'ofth'e excitation currentregulator 60. This produces, via the, input D2 of the vector rotatorVDl, a statorcurrentcomponent parallel to the field which acts in thesame sense as the output signal of the excitation current regulator 60,and aids the "signal'in this manner.

Referring to FIG. 9, the excitation current regulator 60 and the inputcircuit assigned thereto are fed the reference and the actual value ofthe excitation current via input terminals 61, 62. These terminals 61,62 are connected to the input of a differential amplifier 65 so that anydifference between the reference value and actual value of theexcitation current can be obtained therein. The output of thedifferential amplifier 65 is connected with the input of the regulator60 as well as with the terminal 64 which, in turn, is connected with theinput terminal D2 of the vector rotator VDl, as shown in 8. The voltageoutput of the regulator 60 is then passed'to the terminal 63 of acontrol unit St, as above, and thence to the converter 1.

What is claimed is:

l. A method of controlling a converter fed automatically controlledsynchronous machine having a rotor and stator comprising the steps of:

a; ascertaining the sine. and cosine of the instantaneousangularpositionfl of the rotating field axis F of the machine with respect to astator axis system;

b. providing two independently variable reference value components (Iand (l,;*) referenced to the rotating field axis F, I,,-* being acomponent perpendicular to said axis F and 1 being a component parallelto said axis F; and

c. using the values of sineB and cosineB to transform said components Iand l,,*' into'components in said stator axis system to control thevector] of the stator circulation current.

2. In a method as set forth in claim 1 wherein said two components ofsaid rotating-field axis are ascertained directly.

3. In a method as set forth in claim 1 wherein said two componentsofsaidrotating-field axis are field simuv 10 j (sina, cosa) and said twostator-referenced orthogonal stator currentcomponents (i 'i subsequentlyfield simulating said rotor-referenced I stator current components (ii,,) to form two rotor-referenced orthogonal field components (sin p.cosw); and V thereafter combining said rotor-referenced orthogonal fieldcomponents (sin P, cosw) and said orthogonal components (sina, cosa)determining the instantaneous position of the rotor axis to form saidtwo components (sinB, cosB) determining said position of therotating-field axis (F).

5. In an apparatus for controlling a converter-fed automaticallycontrolled synchronous machine having a rotorand a stator;

at least one vector rotator for transforming two components (sinfi,cosB) determining the instantaneous angular position ofthe-rotating-field axis (F) 'of the machine and two independentlyvariable reference-value components (1 I into two statorreferencedorthogonal stator current'components (i,,, i,,), one of said statorcurrent components being perpendicular to saidaxis and the other of saidstator current components being parallel to said axis, said vectorrotator including two summing amplifiers and four multipliers havingoutputs connected in pairs to a respective input of one each of saidamplifiers. 6. In an apparatus as set forth in claim 5 a flux computer(5) including a pair of differential amplifiers (32, 33) and a negativefeedback circuit including resistors therein connected to each saiddifferential amplifier for field simulation said two componentsdetermining the position of .said rotating-field axis; one of saidamplifiers receiving a stator current component (i disposed in thedirection of the rotor axis (P) and a quantity (i proportional to theexcitation current, and the other of said amplifiers receiving a statorcurrent component (i,,) disposed perpendicularly of the rotor axis.

7. In an apparatus as set forth in claim 6 wherein said machine has adamper winding, each said negative feedback circuit connecting an outputof a respective amplifier to an input thereof and including a capacitorand a resistor therein in series.

8. In an apparatus as set forth in claim 7 wherein said flux computerfurther has means (36, 37, 38) for squaring and summing the outputsignals of each differential amplifier to produce an output signal, athreshold stage (41-43) for receiving said output signal and a pair ofmultipliers (34, 35) each multiplier being connected between eachdifferential amplifier and said threshold in a second feedback circuitto receive a signal from said threshold. v

9. In an apparatus 'as set forth in claim8 wherein said flux computer(5) further includes a vector analyzer for receiving the output of saiddifferential amplifiers; said vector analyzer having two quotientgenerators (49,50) for producing output voltages, means (51, 52) forsquaring said output voltages, means (53) for summing said squaredoutput voltages and comparing said summed output voltages with aconstant quantity (E), and an integrating control (54) for receiving acompared voltage from said latter means, said integrating control beingconnected to said quotient generators to deliver an output voltage tosaid generators as a divisor input; and

a vector rotator'connected to said vector analyzer to receive saidoutput voltages of said quotient generators.

10. In an apparatus as set forth in claim 9 wherein said flux computerfurther has a second vector rotator (VD2) therein, a pulse disc (17)coupled to said rotor, a pulse generator (16) connected with said pulsedisc, a digitally operating three-phase generator operatively connectedto said pulse generator to be driven thereby, and a transformationcircuit (16) connected to said three-phase generator for receiving andtransforming three output voltages therefrom into said two components(sina, cosa) determining the instantaneous angular position of saidrotor axis (P), said transformation circuit being connected to saidsecond vector rotator to deliver said latter two components theretoprior to field simulation.

11. In an apparatus as set forth in claim 5 further having atransformation circuit (18) connected to said vector rotator (VDl) toreceive stator-referenced current components (i,,* i,,*) correspondingto field-oriented reference-value components(l 1 three phase currentregulators connected to said transformation circuit to each receive anactual value input; three control units each respectively connected toone of said regulators to transfer a triggering signal from saidregulator, three stator phase leads connected to said stator, and athyristor disposed in each stator phase lead and connected to arespective control unit.

12. In an apparatus as set forth in claim 11, a speed control (56)connected to said rotor to produce a fieldoriented reference valuecomponent (l perpendicular to the rotating field axis (F). I

13. In an apparatus as set forth in claim 12, a quotient generator (59)having a dividend input connected to said speed control, a divisor inputfor receiving a quantity proportional to the absolute value I d) l ofthe rotating-field vector, and an output for emitting saidfield-oriented reference value component (I perpendicular to therotating-field axis (F).

14. In an apparatus as set forth in claim 12, a pulse generator (16)connected to said rotor, a frequencyvoltage converter (57) connectedbetween said pulse generator and said speed control and having an outputconnected to an actual-value input of said speed control.

15. In an apparatus as set forth in claim 14, a flux component (1parallel to the rotating field axis (F).

1. A method of controlling a converter fed automatically controlledsynchronous machine having a rotor and stator comprising the steps of:a. ascertaining the sine and cosine of the instantaneous angularposition Beta of the rotating field axis F of the machine with respectto a stator axis system; b. providing two independently variablereference value components (IW*) and (IB*) referenced to the rotatingfield axis F, IW* being a component perpendicular to said axis F and IB*being a component paralLel to said axis F; and c. using the values ofsine Beta and cosine Beta to transform said components IW* and IB* intocomponents in said stator axis system to control the vector I of thestator circulation current.
 2. In a method as set forth in claim 1wherein said two components of said rotating-field axis are ascertaineddirectly.
 3. In a method as set forth in claim 1 wherein said twocomponents of said rotating-field axis are field simulated.
 4. In amethod as set forth in claim 3 the steps of determining theinstantaneous position ( Alpha ) of the rotor axis and forming twoorthogonal components (sin Alpha , cos Alpha ) determinitive thereof;obtaining two stator-referenced orthogonal stator current components(ia, ib); forming two rotor-referenced stator current components (id,iq) from said two orthogonal components (sin Alpha , cos Alpha ) andsaid two stator-referenced orthogonal stator current components (ia,ib); subsequently field simulating said rotor-referenced stator currentcomponents (id, iq) to form two rotor-referenced orthogonal fieldcomponents (sin , cos ); and thereafter combining said rotor-referencedorthogonal field components (sin , cos ) and said orthogonal components(sin Alpha , cos Alpha ) determining the instantaneous position of therotor axis to form said two components (sin Beta , cos Beta )determining said position of the rotating-field axis (F).
 5. In anapparatus for controlling a converter-fed automatically controlledsynchronous machine having a rotor and a stator; at least one vectorrotator for transforming two components (sin Beta , cos Beta )determining the instantaneous angular position of the rotating-fieldaxis (F) of the machine and two independently variable reference-valuecomponents (IW, IB) into two stator-referenced orthogonal stator currentcomponents (ia, ib), one of said stator current components beingperpendicular to said axis and the other of said stator currentcomponents being parallel to said axis, said vector rotator includingtwo summing amplifiers and four multipliers having outputs connected inpairs to a respective input of one each of said amplifiers.
 6. In anapparatus as set forth in claim 5 a flux computer (5) including a pairof differential amplifiers (32, 33) and a negative feedback circuitincluding resistors therein connected to each said differentialamplifier for field simulation said two components determining theposition of said rotating-field axis; one of said amplifiers receiving astator current component (id) disposed in the direction of the rotoraxis (P) and a quantity (ie) proportional to the excitation current, andthe other of said amplifiers receiving a stator current component (iq)disposed perpendicularly of the rotor axis.
 7. In an apparatus as setforth in claim 6 wherein said machine has a damper winding, each saidnegative feedback circuit connecting an output of a respective amplifierto an input thereof and including a capacitor and a resistor therein inseries.
 8. In an apparatus as set forth in claim 7 wherein said fluxcomputer further has means (36, 37, 38) for squaring and summing theoutput signals of each differential amplifier to produce an outputsignal, a threshold stage (41-43) for receiving said output signal and apair of multipliers (34, 35) each multiplier being connected betweeneach differential amplifier and said threshold in a second feedbackcircuit to receive a signal from said threshold.
 9. In an apparatus asset forth in claim 8 wherein said flux computer (5) further includes avector analyzer for receiving the output of said differentialamplifiers; said vector analyzer having two quotient generators (49, 50)for producing output voltages, means (51, 52) for squaring said outputvoltages, means (53) for summing said squared output voltAges andcomparing said summed output voltages with a constant quantity (E), andan integrating control (54) for receiving a compared voltage from saidlatter means, said integrating control being connected to said quotientgenerators to deliver an output voltage to said generators as a divisorinput; and a vector rotator connected to said vector analyzer to receivesaid output voltages of said quotient generators.
 10. In an apparatus asset forth in claim 9 wherein said flux computer (5) further has a secondvector rotator (VD2) therein, a pulse disc (17) coupled to said rotor, apulse generator (16'') connected with said pulse disc, a digitallyoperating three-phase generator (15) operatively connected to said pulsegenerator to be driven thereby, and a transformation circuit (16)connected to said three-phase generator for receiving and transformingthree output voltages therefrom into said two components (sin Alpha ,cos Alpha ) determining the instantaneous angular position of said rotoraxis (P), said transformation circuit being connected to said secondvector rotator to deliver said latter two components thereto prior tofield simulation.
 11. In an apparatus as set forth in claim 5 furtherhaving a transformation circuit (18) connected to said vector rotator(VD1) to receive stator-referenced current components (ia* , ib*)corresponding to field-oriented reference-value components(IW*, IB*);three phase current regulators connected to said transformation circuitto each receive an actual value input; three control units eachrespectively connected to one of said regulators to transfer atriggering signal from said regulator, three stator phase leadsconnected to said stator, and a thyristor disposed in each stator phaselead and connected to a respective control unit.
 12. In an apparatus asset forth in claim 11, a speed control (56) connected to said rotor toproduce a field-oriented reference value component (IW*) perpendicularto the rotating field axis (F).
 13. In an apparatus as set forth inclaim 12, a quotient generator (59) having a dividend input connected tosaid speed control, a divisor input for receiving a quantityproportional to the absolute value ( phi ) of the rotating-field vector,and an output for emitting said field-oriented reference value component(IW*) perpendicular to the rotating-field axis (F).
 14. In an apparatusas set forth in claim 12, a pulse generator (16'') connected to saidrotor, a frequency-voltage converter (57) connected between said pulsegenerator and said speed control and having an output connected to anactual-value input of said speed control.
 15. In an apparatus as setforth in claim 14, a flux control (4) for controlling the rotorexcitation, said flux control receiving a quantity proportional to theabsolute value of the rotating-field vector as an actual value.
 16. Inan apparatus as set forth in claim 15, an excitation current regulator(60) subordinated to said flux control (4).
 17. In an apparatus as setforth in claim 16 wherein said excitation current regulator (60)receives an input signal determining said field-oriented reference-valuecomponent (IB*) parallel to the rotating field axis (F).